fix(fs): remove temporary file when compression fails (#2264)

compressFileNolock created a ".tmp" file but left it on disk when the
compression copy, os.Chtimes, or os.Rename step failed, leaking partial
files that accumulate over time. Remove the temporary file in each error
path.

Fixes #2239

Signed-off-by: Y.Horie <u5.horie@gmail.com>

fs.go

@@ -1740,13 +1740,16 @@ func (h *fsHandler) compressFileNolock(
 	_ = zf.Close()
 	_ = f.Close()
 	if err != nil {
+		_ = os.Remove(tmpFilePath)
 		return nil, fmt.Errorf("error when compressing file %q to %q: %w", filePath, tmpFilePath, err)
 	}
 	if err = os.Chtimes(tmpFilePath, time.Now(), fileInfo.ModTime()); err != nil {
+		_ = os.Remove(tmpFilePath)
 		return nil, fmt.Errorf("cannot change modification time to %v for tmp file %q: %v",
 			fileInfo.ModTime(), tmpFilePath, err)
 	}
 	if err = os.Rename(tmpFilePath, compressedFilePath); err != nil {
+		_ = os.Remove(tmpFilePath)
 		return nil, fmt.Errorf("cannot move compressed file from %q to %q: %w", tmpFilePath, compressedFilePath, err)
 	}
 	return h.newCompressedFSFile(compressedFilePath, fileEncoding)

fs_test.go

@@ -3,8 +3,10 @@ package fasthttp
 import (
 	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
+	iofs "io/fs"
 	"math/rand"
 	"os"
 	"path/filepath"
@@ -882,6 +884,42 @@ func runFSCompressSingleThread(t *testing.T, fs *FS) {
 	testFSCompress(t, h, "/README.md")
 }
 
+// errReadFile is an fs.File whose Read always fails, used to force the
+// compression step in compressFileNolock to return an error.
+type errReadFile struct {
+	fi iofs.FileInfo
+}
+
+func (f *errReadFile) Stat() (iofs.FileInfo, error) { return f.fi, nil }
+func (f *errReadFile) Read([]byte) (int, error)     { return 0, errors.New("forced read error") }
+func (f *errReadFile) Close() error                 { return nil }
+
+func TestFSCompressTmpFileRemovedOnError(t *testing.T) {
+	t.Parallel()
+
+	dir := t.TempDir()
+
+	// Use this test file as the source for a valid fs.FileInfo.
+	fi, err := os.Stat("fs_test.go")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	h := &fsHandler{}
+	compressedFilePath := filepath.Join(dir, "out.gz")
+	tmpFilePath := compressedFilePath + ".tmp"
+
+	_, err = h.compressFileNolock(
+		&errReadFile{fi: fi}, fi, "fs_test.go", compressedFilePath, "gzip")
+	if err == nil {
+		t.Fatalf("expecting error when compression fails")
+	}
+
+	if _, err := os.Stat(tmpFilePath); !os.IsNotExist(err) {
+		t.Fatalf("temporary file %q must be removed on compression error, stat err: %v", tmpFilePath, err)
+	}
+}
+
 func testFSCompress(t *testing.T, h RequestHandler, filePath string) {
 	t.Helper()